1. Field of the Invention
The present invention generally relates to a cryogenic refrigerator which generates cold (a cold thermal energy causing an ultra-low temperature) by generating Simon expansion using a high-pressure refrigerant gas supplied from a compression device.
2. Description of the Related Art
For example, the Patent Document 1 discloses a Gifford-McMahon (GM) refrigerator causing a gas existing inside a gap between a piston of the GM refrigerator and a cylinder of the GM refrigerator to expand. The GM refrigerator includes a linear groove extending in an axial direction which functions as an orifice.    [Patent Document 1] Chinese Laid-open Patent Publication No. 101900447A